Investment Securities (Schedule Of FHN's Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale	$ 4,826,155	$ 5,170,255
Pledged available for sale securities	4,100,000	4,000,000
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, Amortized cost	10,000	10,000
Securities held to maturity, Gross Unrealized Gains	0	0
Securities held to maturity, Gross Unrealized Losses	(183)	(99)
Held-to-maturity Securities, Fair Value	9,817	9,901
FRB
Schedule of Available-for-sale Securities [Line Items]
Restricted investments		134,600
FHLB-Cincinnati Stock
Schedule of Available-for-sale Securities [Line Items]
Restricted investments		87,900
Interest- only strips- AFS
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale	2,733	1,270
Corporate Bonds
Schedule of Held-to-maturity Securities [Line Items]
Securities held to maturity, Amortized cost	10,000	10,000
Securities held to maturity, Gross Unrealized Gains	0	0
Securities held to maturity, Gross Unrealized Losses	(183)	(99)
Held-to-maturity Securities, Fair Value	9,817	9,901
U.S. treasuries
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	100	100
Securities available for sale, Gross Unrealized Gains	0	0
Securities available for sale, Gross Unrealized Losses	(2)	(1)
Securities available-for-sale	98	99
Government agency issued MBS
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	2,585,250	2,580,442
Securities available for sale, Gross Unrealized Gains	6,384	10,538
Securities available for sale, Gross Unrealized Losses	(60,772)	(13,604)
Securities available-for-sale	2,530,862	2,577,376
Government agency issued CMO
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	2,266,776	2,302,439
Securities available for sale, Gross Unrealized Gains	984	1,691
Securities available for sale, Gross Unrealized Losses	(61,419)	(34,272)
Securities available-for-sale	2,206,341	2,269,858
Equity and other
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	29,822	265,863
Securities available for sale, Gross Unrealized Gains	0	7
Securities available for sale, Gross Unrealized Losses	(199)	0
Securities available-for-sale	29,623	265,870
Corporates and other debt
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	55,716	55,799
Securities available for sale, Gross Unrealized Gains	587	23
Securities available for sale, Gross Unrealized Losses	(315)	(40)
Securities available-for-sale	55,988	55,782
States and municipalities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	512
Securities available for sale, Gross Unrealized Gains	0
Securities available for sale, Gross Unrealized Losses	(2)
Securities available-for-sale	510
Securities available-for-sale, excluding interest only strip:
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	4,938,176	5,204,643
Securities available for sale, Gross Unrealized Gains	7,955	12,259
Securities available for sale, Gross Unrealized Losses	(122,709)	(47,917)
Securities available-for-sale	$ 4,823,422	$ 5,168,985

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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The fair value of available-for-sale securities that serve as collateral for borrowings.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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